1. Field of the Invention
The present invention relates to a sheet conveyance apparatus used in an image forming apparatus, such as a copying machine, a printer, or a facsimile, and also relates to an image forming apparatus including this sheet conveyance apparatus.
2. Description of the Related Art
Conventionally, the sheet conveyance apparatus applied to an image forming apparatus conveys a sheet along a sheet conveyance path formed by a pair of sheet guide plates facing to each other. When a thin sheet is conveyed in this sheet conveyance apparatus, the sheet tends to stick to the guide plates due to water vapor or static electricity. Particularly, immediately after a toner image is thermally fixed, since a lot of water vapor is produced from the sheet, the sheet has a high chance of sticking to the sheet guide plates. To prevent the sheet from sticking to the sheet guide plates, a contact area between the sheet and the sheet guide plate needs to be reduced. Therefore, a sheet conveyance apparatus provided with protrusions from the sheet guide plates (sheet guide ribs) has been devised.
Meanwhile, when a thick sheet is conveyed in the sheet conveyance apparatus provided with the sheet guide ribs, there is a possibility that a sheet gets scratched by the ribs or an image formed on the sheet is distorted.
As a consequence, a sheet conveyance apparatus has been developed which can adjust projecting amounts of the sheet guide ribs to deal with thin and thick sheets (Japanese Patent Application Laid-Open No. 2008-120568).
However, in the sheet conveyance apparatus according to Japanese Patent Application Laid-Open No. 2008-120568, when adjusting the projecting amount, a user is required to set and input a thickness of a sheet to be conveyed. Therefore, substantial time and labor is required in performing settings, so that setting errors and forgetting are likely to occur.
Another problem is that a drive source needs to be provided for a device to adjust the projecting amount of the sheet guide ribs, which is likely to increase the size of the apparatus.